The complex‐variable boundary element method (CVBEM) is used to analyse forced convection in cooling passages with general, convex cross‐sections. Quadratic spline interpolation is employed for the modelling of coupled velocity and temperature fields. The method is well‐suited for ducts with curved surfaces and high geometric aspect ratios. The method is illustrated for ducts with rounded rectangular, elliptical and rounded diamond cross‐sections. General correlations are presented for the fully developed Nusselt number and Moody friction factor, and the Hagenbach entrance region factor. Copyright © 1999 John Wiley & Sons, Ltd.